Heat detection apparatus



April 6, 1965 J. E. LINDBERG HEAT DETECTION APPARATUS Filed NOV. 23, 1962 INVENTOR. JOHN E. LINDBERG BY (9w, mm b 22144 ATTORNEY indicator at the fire station.

United States Patent This invention relates to an improved apparatus for heat detection and especially fire detection. l fore particularly it relates to a heat-detection system having integrity test means, and to a heat-detection system without electrical relays.

The present invention is an improvement of the apparatus described and claimed in my-copending application Serial No. 102,622, filed April 10, 1961, now abandoned. That application provides a novel non-electric heat-detecting element or sensor located in a heat-detection Zone and connected outside the zone to an electrical warning or corrective system by a novel instrument called a responder. The sensor may be filamentary-a long, very-narrow-diameter, hollow tube, which may extend along a line, around a circle, or along any desired path and for practically any desired length. Also, the actual alarm or heat-condition indicator can be connected to the responder by a wire of practically any desired length.

For example, the heat-detecting sensor may be inside a house, the responder just outside the house, and the 01', the non-electric heatdetecting sensor may be in zone 1 of an aircraft engine ahead of a fire wall, the responder may be behind the fire wall, and the indicator may be on the aircraft instrument panel.

'Conventional fire detectors employed in aircraft for zone-l fire detection, whether of the continuous type or of the single-point type, have been liable to give false alarms. For example, a prevailing type of continuous fire detector is actuated by the change in electrical resistance of semi-conducting materials caused by a change in environmental temperature. Moisture, however, can

produce the same efifect as high temperatures. Moisture conditions in the engine chambers, where zone-1 detectors are located, vary considerably, because changes in altitude radically affect the temperature and pressure conditions there. As a consequence, moisture condensation occurs frequently and has often caused these electrical firedetectors to develop low-resistance shorts that resulted in false alarms. False alarms are seriousenough on the ground, as everyone knows, but in aircraft they are unforgivable, because the crew must immediately take hazardous and expensive emergency action.

The present invention solves the false-alarm problem. Like the device described in application Serial No. M32622, the sensor is never actuated by moisture or by atmospheric conditions. In addition, it includes an improved circuit and a greatly improved testing apparatus. Such troubles as poor electrical connections at the joints between successive elements of continuous-type detectors, and the accumulation of foreign material in the connections, both leading'to heating at the joints, cannot occur this invention. My invention uses only the simplest electrical connections.

Some prior-art types of fire detectors have given false alarms because they responded to the rate of change of temperature rather than, or in addition to, a predetermined high temperature level. Consequently, during airplane takeoii, when the temperature in the power-plant area was increasing very rapidly, these detectors sometimes gave false alarms when everything was normal. The same thing happened during rapid climbing and some other operating conditions. The device of this invention is not affected by the rate of change of temperature; so another source of false alarms is eliminated.

Prior-art continuous-type fire detectors also gave false alarms whenever the detector element was seriously damaged, because short circuits were then caused within the element. The sensor of the present invention can be completely severed, cut open, dented, or bent in any fashion without causing a false alarm. Moreover, the integrity test device discloses whether the sensor is operable or inoperable.

A very important object of the invention is to provide means for giving a complete test of the unit. The test is positive; if the test shows that the unit will work, the unit will work, and if it shows that the unit will not work, the unit will not work.

A further object is to provide a fire detector capable of indefinitely recycling to give warning each time a critical elevated temperature is reached and to withdraw the warning each time the temperature drops.

Another object is to provide a completely herm tically sealed heat-detection transducer, completely free from environmental errors caused by such things as pressure and altitude changes, moisture condensation, and so on. 7 Another object is to provide a fire-detection system which avoids the complexities characteristic of other fire detectors. For example, no amplifiers or relays need be used in this system. This solves an important problem,

ecause heretofor lire detection systems for a fourengine airplane have required more than ten relays, each heavy, each an expense.

Another object of the invention is to enable the use of several non-electric heat-detecting transducers in combination with a single electrical circuit, to achieve simplicity while still pinpointing which transducer has been actuated.

Other objects and advantages of the invention will appear from the following description of some illustrative embodiments thereof.

in the drawings:

FlG. 1 is an enlarged View in elevation and partly in section of a sensor-responder unit embodying the principles of the invention; since a typical sensor is in the order of twenty feet long, it has been broken in a few places to conserve space but in actual practice it is continuous.

FIG. 2 is an enlarged fragmentary view in elevation and partly in section of a portion of the sensor of FIG. 1.

H6. 3 is a partly diagrammatic view in elevation of a simple circuit utilizing the sensor-responder unit of FIG. 1.

As shown in FIG. 3, the fire-detection system of this invention preferably comprises (1) a non-electric detection means, preferably in the form of a generally filamentary sensor A of some desired length, (2) a responder B, and (3) an electrical circuit C. The function of the sensor A is to actuate the responder B, which in turn actuates the electrical circuit C. Thus, the sensor A constitutes a heat-to-pressuretransducing means, while the sensor A and the responder B, considered together, comprise a heat-toelectric-current transducer.

The sensor A may be further defined in general terms (see PlGS. 1 and 2) as a generally filamentary enclosure D of extended length connected to the responder B and containing means E responsive to heat in the environment of the sensor A, for raising the internal pressure in the responder B. The responder B is a type of pressure-actuated electrical switch that opens or closes in response to the pressure changes induced by the response of the sensor A to heat. The electrical circuit C may be a warning circuit or a remedial circuit.

The system of this invention has many features especially suitable to use in aircraft. Just to give a general dride, thoughitis nota :stoichiometric compound.

. and molybdenum, for example.

ner surfacs of the tube D should'not react -with them'amay lead to warning lights fand bells on :the aircraft instrument panel.

' V I. 3,177,479 I Preferably,.the tube-Dv is of. metal, is gas tight, is narrow in diameter and has a constant cross-sectional area over its length. Withinthis tube D,.the. means E is'responsive to the temperature of-;the tube D for varying the pressure inside the tube.

ting agent. :The enclosure D is connected to the responder B,..which1itself defines 'a closed chamber connected to the' enclosure D. An alteration of the internal pressure within the enclosure D therefore affects the internal pressure within the responder. B.' a a a This invention preferably employs as transducing agents E metallichydrides thatretain hydrogen at low temperatures and emit hydrogen gas progressively over a wide 1-a andtI I- a of the periodic table, hydrogen forms stoichiometric compounds such as sodium hydride and calcium hydride. These are'ionic in behavior, with hy drogen as the'negative ion. The reactions are reversible and exothermic; Specificallyrhydrogen reacts with lithium, sodium, potassium, rubidium, cesium, francium, calcium, strontium, bariunnand radium: in stoichiornetric proportions to form hydrides. With the elements of This means E may also be termed a transducing agent or a gas-transfer or gas-ennt- .20 range of elevated temperatures. These are set out-in detail in my copending application. Serial No. 102,622, 7 towhich reference may be had for complete details;- With the alkali andalkaline earth metals, i.e., groups 4 7 a filament Iii-ribbon 1'1 rcombinationis used in mostof the length of the sensor A of FIG. 1.

The new departure in the present invention is the provision, preferably at or near the end 13 of the tube D distant from the responder B, of a short length (e.g., about one foot in a sensor A' that is twenty feet long) of a filament 14 of a metal which also ingasses and outgasses hydrogen butwhich has an outgassing temperature substantially lower than that of the metal comprising the main detecting filament 10. For example, if the filament .10 is zirconium, the filament 14 may be titanium or palladium. (If it is titanium, it will be wrapped V toprovide a gas-tight sea1,'while the other end 13, of the Q tube'D is still open.

I This free end 13 may be purged and evacuated. Then the tube D is heated, and pure hydrogen is forced in;through the free end 13; the tube D is cooled, and both the filamentsli) and 14 absorb hydro- .gen while cooling, so. that the originally pure metals 10 I and 14 are converted into ingassed hydrides having some groups,III-a (includingthe'rare earthand actinideelef f ments),*IV-a andV-a, and with palladium, hydrogen forms-pseudo-hydrides. The solubility of hydrogen in elements of these groups varies as the square root of the pressure, and it decreases with increase in temperature.

This class consists of scandiurn, titanium, vanadium, V;

ytterbium, zirconium, niobium, hafnium, tantalum, the rare earth metals (atomic numbers 57 through 7 1), the

actinide metals (atomic numbers 89 through 103), and.

palladium. This solutionis commonly termed 'a hy- .My co-pending application, Serial No. 102,622, illustratesa few of themany ways in which the sensor A may be constructed. TransducingagentsE may be .used in a filamentary pellet,: or. granular form, always being placed inside thesensor tube D, which is anon-porous ,what different properties. The free end 13 is then sealed off as by.inserting'a brazing wire 17 and fusing it to the tube D, and the device is ready. for operation except for the electrical wiring;

FIG. '1 shows one preferred form of responder B. 'This "responder B has a thin flexible metal (e.g., molybdenum 'or"Kovar) disc or diaphragm 20 brazedbetween two circular plates 21 and 22, of non porousmetal, preferably molybdenum,or"Kovar. (According to Handbook of Material Trade Names, 1953 'Edition, published by Industrial} Research Service. at,Dover, New Hampshire, ;Kovar is a registered trademark for an alloy of 20% nickel, 17% cobalt, 0.2% manganese, and the, balance 7 iron.) The plates 21. and 22' are hermetically sealed to electrically conductive tube, preferably of constantcross- 5':

terials itcontacts, including the gas involved. Atypical sensor tube D is preferably about 0.040" to 0.060" but- Suitable 1 metals are nickel, pure iron:

In any event, the in; J

the diaphragm and are in electrical contact therewith for their. full peripheries and over a; substantial margin. In its center the diaphragm. 20 has a generally sphericalsegment depression 23: called a blister, which is free to move relative to the plates 21 and22 and constitutes the offanupperplate 21 with a planarlower surface 23 and side diameter with a wall thickness of preferably about 7 shorter.

FIG. 2 shows a portion of one preferred form of transtitaniumorcalcium Wire, and may be about 0.025. to

0.050" ill diameter, for example. A ribbon 11 of 'suitable material, such as-molybdenum or tungsten, preferably about 0.020 wide'and 0.002 thick, is wrapped 7 Such tubes D are preferablyabout. two to 'thirty feet long, although'they may be longer" or gives amore predictable response,but other diaphragm structures may be used ,where feasible. The lower plate 22Lis-formed with a, recess 25 in its upper surface, and the diaphragm 20"divides'the resultant cavity between theplates Hand 22 into two regions or chambers 26 and 27. Since the lower region 26" communicates. with the sensorA,'it rnaybe called the sensor chamber. The other region 26 is located on the opposite side of the diaphragm 20 from the sensor A; so it may be called the anti-sensor chamber. The sensor chamber 26 is closed and sealed'except for its communication with the lumen tightly around the filamentary transducing agent '10, The

ribbon 11 physically spacesthe filament 10 fromicontact with the inside wall 12 of the tube. D and prevents the transducing agent 10 from fusingorwelding to the I tube walls 12, even ;in the event thatithezgsensor'A is exposed to extreme'heat jand even jif the filament lfljis I of the sensor tube D; so the inside of the sensor A and the sensor chamber 26 enjoy a common atmosphere to the exlusion of any other. s

A tube 28 of non-porous ceramic material or other nonporous electrically-insulating material extends through a stepped opening 29 provided by a metal tube. 30 that. is brazed into the upper plate'21 flush with the surface 24, the "tube'28 being hermetically sealed in place with its .lower' end 31 fiush 'with the bottom surface 24 vof the fully'ing asse'd, so that it is enlarged to nearly the internal diameter of the tube D. f- The invention as so far describedis that of application Serial No. 102,622,;andsuch I plate :21. The hole 29 and tube 28 are preferably centered with respect to the'blister 23. 1A metal rod 32, preferably of molybdenum, lies inside the tube 28 and serves as an electrode 'witha tip ,or contact portion 33 of the rod 32 The reasons for lying flush with (or very slightly below) the lower surface 24 of the plate 21. When sufiicient pressure is applied to the sensor side of the blister 23, the blister is deflected and makes contact with the electrode portion 33, and when the deflecting force is removed, the restoring force of the blister 23 returns it to its relaxed position and thus breaks contact with the electrode portion 33. The force necessary to deflect the blister 23 may be chosen by proper design to accommodate a wide range of values.

The outer end of the molybdenum rod 32 is preferably drilled axially to provide a receptacle 34 within which fits the end of a nickel capillary tube 35, which is secured to the rod 32, as by a cuplat braze, at a location short of the lower end 36 of the receptacle. A hole 37 extends radially through the wall of the receptacle 34 in between the receptacle end 36 and the end of the tube 35. A cap 38, preferably of Kovar or molybdenum, is brazed to the ceramic tube 23 and to the capillary tube 35, and the lengths of the tubes 28 and 35 and the rod 32 are carefully chosen to match the coeflicients of expansion and the lengths of the two metal members 32 and 35 to the coefficient of expansion and the length of the member 23. It is important to keep the lower end 33 or the contact rod 32 from moving above the surface 24 of the plate 21. With the relative lengths of the molybdenum and nickel parts chosen so that their expansion and contraction exactly cancel those of the ceramic tube 28, whose coefiicient of expansion lies between those of nickel and molybdenum, this distance is easily maintained.

The cylindrical rod 32 of molybdenum fits fairly snugly into the bore of the ceramic tube 28, while still leaving sumcient clearance for gas passage. The radial hole 37 enables passage of hydrogen gas or a mixture of hydrogen and a noble gas, such as argon or neon, through the capillary tube 35 into the ceramic tube 28. Hence, the nickel tube 35 may be used to introduce gas under pres sure into the anti-sensor chamber 27 to provide any desired pressure there, with resultant effect on the response characteristics of the blister 23. It may then be closed oil by inserting a wire 39 in its outer end and brazing it to the tube 35. Then the tube 35 may be brazed to an electrical jack or socket member 4a. Thus, when the blister 23 contacts the electrode 33, electric current can pass from the blister 23 to the rod 32, the tube 35', and the socket 44b, to which the electric warning circuit C is connected.

A simple electrical warning circuit C is shown in FIG. 3. It will be seen that a lead 41 connects the socket 4t) to two lamps 42 and 43 in parallel with each other and in series with the lead 43. and a lead 44, which leads to one side of a battery 45. A lead 46 connects the other side of the battery 45 to a terminal 47, which may be on either plate 21 or 22 of the responder B.

When the blister 23 is not in contact with the electrode 33, the circuit through the battery 45 is open, and it cannot light the lamps 42 and 45. Whenever there is a fire or heat condition such as to emit sufilcient gas inside the sensor A, the pressure in the sensor chamber 26 builds up and closes the blister 23, against the electrode 33, closing the circuit through the battery 45 and lighting the signal lamps 42 and 43.

The importance of the filament 1-4 which differentiates the sensor A of this invention from that of Serial No. 102,622, is in the test circuit F. A terminal 5% on the far end 13 of the sensor tube D is connected by a lead 51 to a test switch 52, which is connected to a second battery 53. The other side of the battery 53 may be grounded and a point 54 on the tube D just at the end of the filament 14 may also be grounded, so that when the switch 52 is closed, the filament 14 is heated and will outgas. The same thing may be achieved by connecting the other side of the battery 53 to the point $4 in a closed circuit. The battery power may be so adjusted that it heats the filament 14 but does not heat the filament Ilil above the outgassing temperature.

For testing the circuit of FIG. 3', the switch '52 is closed. The sensor portion 14 is then heated electrically by the current passing from the battery 53 directly through a segment 55 of the metal tube D that surrounds the filament 14. I may, however, use any other suitable means for heating only the segment 55 and the portion 14 electrically. The heat is not uniformly distributed along the sensor A, but is concentrated at the filament 14. The sensor A is adjusted so that when the filament 14 is thus heated, it gives oil enough hydrogen to increase the pressure in the tube D by an amount that will sutlice to move the biister 23 against the electrode tip 33. If, however, the responder B is inoperative or if the sensor tube D leaks, or the system is for any reason inoperative, this fact will be disclosed by the non-operation of the test circuit. If and only if the system does work and is integral, the responder B completes the alarm circuit, lighting the warning lamps 42 and 43.

It there is a break in the sensor A or if the circuit C is broken or if there is a fault in some other part of the system, the warning lamps 42 and 43 will not light during the test, indicating that something is wrong with the system. Since it is the gas pressure in the sensor A which actuates the responder B during the test cycle, this test method gives a true test of the entire fire detector system by producing actual high temperature conditions in the sensor. By having the filament l4 outgas at a lower temperature than the filament lit}, the main filament lit is completely unaiiected by the test.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely iHustrative and are not intended to be in any sense limiting.

I claim:

1. lo a critical-temperature-detcction system having a heat detecting sensor of extended length and signal means actuated by said sensor when a critical temperature is reached at any point along its length, the combination therewith of said sensor having a first long major portion and a second short portion and a test circuit including means for heatin said short portion of said sensor to its critical temperature and thereby causing actuation of said signal means.

2. The system of claim 1 wherein said sensor main portion responds at one critical temperature and a test portion in said short portion responds to a lower critical temperature.

3. In a critical-temperattire-detection system having a heat detecting sensor of extended length, said sensor having a first, longer portion and a second portion that is short relative to said first portion, a'pressure switch connected to one end of said sensor and closed by pressure generated in said sensor as a result of any segment along said sensor being heated to said critical temperature, and signal means actuated by closure of said switch, the combination therewith of a test circuit including means for heating said short second portion of said sensor to its critical temperature and thereby causing closure of said switch.

4. The system of claim 3 wherein said short second portion is the portion of said sensor most distant from said switch so that the pressure generated there passes through the rest of said sensor in order to actuate said switch.

5. The system of claim 3 wherein said sensor main portion responds at one temperature and a test portion in said short second portion at the end distant from said switch responds to a lower temperature.

6. A critical-temperattire-detection system comprising an imperforate electrically conductive enclosure of 'extended length;

first heat-to-pressure transducing means for substantially increasing the pressure withinsaid enclosure when said enclosure is externally heated above a first predetermined temperature; second heat-to pressure transducing means in one end of said enclosure and substantially increasing .the

pressure within said enclosure when the end portion it is in is heated to an actuation temperature below that required to activate said first transducing means;

pressure-actuated switch means atthe opposite end of said enclosure actuated by the pressure insaid en,

closure; an electrical warning circuit source of electrical curent, signal 'means,'said switch means, and return means from said switch means tosaid source, so that when said switch means is closed by a pressure increase in said enclosure it causes said circuit to actuate-said signal means; and

a test circuit including means for sending current through said end portion of said enclscure within which said second transducing meansis located, for electrically heating said secondtr'ansducing means and thereby'causing closure, of said switch means and therefo re actuation of said signal means.

' '7.'A critical-temperature-detection system comprising an imperforateelectrically conductive'enclosure of extended length; i

a first metallic hydride in said enclosure and-occupying a major portion of said length and outgassing'toinincluding, in series, a-

crease the pressure within said enclosure when said enclosure is externally heated to a first critical temperature;

V a second metallic hydride in one end of enclosure and occupying aminor portion of said length and outgassing to substantially increase the pressure within said enclosure when the end portion it is in is heated to a second critical temperature below said first critical temperature; 1

- pressure-actuated switch means at theopposite 'end of said enclosure actuated by 'the pressure in said enclosurley V a an electrical 'warning circuit including, in series, a source of electrical current, signal means, said switch means, and'return means from said switch meansto said source, so that when said switch means is closed by a pressure increase in said enclosure it causes said 7 circuit to actuate said signal means; and

' a test circuit including means for sending current through said end portion of said enclosure within 7 which said second hydride is located, for electrically heating" said second hydride and thereby causing closure of said switch means and therefore actuation of said signal means. I

. References Cited in the'file of this patent UNITED STATES 'PATENTS 

1.
 1. IN A CRITICAL-TEMPERATURE-DETECTION SYSTEM HAVING A HEAT DETECTING SENSOR OF EXTENDED LENGTH AND SIGNAL MEANS ACTUATED BY SAID SENSOR WHEN A CRITICAL TEMPERATURE IS REACHED AT ANY POINT ALONG ITS LENGTH, THE COMBINATION THEREWITH OF SAID SENSOR HAVING A FIRST LONG MAJOR PORTION AND A SECOND SHORT PORTION AND A TEST CIRCUIT INCLUDING MEANS FOR HEATING SAID SHORT PORTION OF SAID SENSOR TO ITS CRITICAL TEMPERATURE AND THEREBY CAUSING ACTUATION OF SAID SIGNAL MEANS. 